In the fabrication process for integrated circuit devices, various chemicals including gases and liquids are utilized. One of such gases utilized more recently as a reactant in a silicon oxide deposition process or a cleaning agent for wafer surfaces is ozone. For instance, silicon oxide films can be deposited onto semiconductor wafers at atmospheric pressure and at a low deposition temperature by reacting tetraethoxysilane (TEOS) with ozone. Ozone is used as an reactant to produce films which exhibit smooth profiles over steps and therefore can be used to fill high aspect ratio gaps between metal lines. Silicon oxide films produced by ozone and TEOS is most suitable for inter-metal dielectrics.
Ozone has also been used as an effective cleaning agent for wafer surfaces. For instance, after a photolithographic process, a photoresist layer is usually stripped by a combination of a dry ashing process with ozone and then wet cleaned by H.sub.2 SO.sub.4 /H.sub.2 O.sub.2. In the process, most of the organic residue from photoresist can be removed in the ozone ashing process while the wet cleaning is used to render the wafer surface completely clean. In another process that utilizes ozone for cleaning, ultrapure water injected with ozone is also used to clean wafer surfaces. In the process where ozone is first dissolved in ultrapure water, ozone decomposes and becomes a strong oxidizing agent which is capable of decomposing organic impurities. The ozone-injected ultrapure water cleaning process therefore provides the advantages of lower cleaning temperature, simplified process, and reduced chemical consumption and waste. There is, however, a side effect with the ozone cleaning process in that native oxide may grow on the wafer surface at high ozone concentrations. After an ozone cleaning process is conducted on a wafer surface, the organic contaminant-free surface resulting from the ozone treatment further helps subsequent cleaning steps to function properly. Overall, the ozone-injected ultrapure cleaning process is an effective method to remove all organic impurities on a wafer surface. It can be carried out at room temperature and can be used to replace a conventional H.sub.2 SO.sub.4 /H.sub.2 O.sub.2 wet cleaning process.
Ozone is a triatomic allotrope of oxygen which has a characteristic pungent odor. Ozone is produced naturally in the earth's stratosphere by the absorption of solar radiation into oxygen. Ozone is also present in the earth atmosphere in low concentration as a consequent of intrusions of stratospheric air. Since ozone exists in an unstable state, it decomposes into oxygen at normal temperature and pressure. Such characteristic enables ozone to be a powerful oxidizing agent. Its strong ability to oxidize has therefore been utilized in the fabrication processes for integrated circuit devices whenever an oxidation process is desired.
In a semiconductor fabrication facility, ozone is normally generated by a silent discharge method such that a large quantity of ozone in higher concentration can be produced for production used. In the silent discharge technique, an oxygen gas is passed through inbetween two electrodes which are coated by a ceramic dielectric material and are separated with a narrow gap formed inbetween. Such an electrode arrangement is known as a discharge cell. The reaction to form ozone can be initiated when a voltage is applied to the discharge cell. Oxygen molecules are decomposed into oxygen atoms from the collisions between the electrons and the oxygen molecules. The active oxygen atoms then recombine with surrounding oxygen molecules to form ozone. The reaction can be expressed as 3 O.sub.2 .fwdarw.2 O.sub.3. The ozone synthesis process proceeds in an equilibrium chemical reaction. The reaction rate increases as the reaction temperature is increased. Since most of the energy applied to the discharge cell is converted to heat and that if the heat is not removed, the ozone produced will be destructed at the high temperature. As a consequence, the discharge cell for ozone production must be cooled efficiently by a heat exchanger method.
In order to supply a large enough volume for ozone of production use in a semiconductor fabrication plant, a series of ozone generators (or ozone generating cells) are connected together in parallel so that a high concentration and large volume of ozone can be generated as a reliable supply to a deposition or a cleaning process. With the increasing number of ozone generating cells used, the chances of having ozone leaks from one or more of the cells become significantly higher. When ozone leaks from a generating cell in a semiconductor fabrication plant, several problems can occur due to the leakage. First, since ozone breaks down easily into oxygen at normal temperature and pressure, and oxygen can help combustion of many flammable materials which are frequently used in a semiconductor fabrication plant, the ozone leakage presents a fire and explosion hazard. Secondly, the inhalation of ozone into human body may also produce various health hazards that may be detrimental to the plant workers. The ozone gas has an unpleasant, pungent odor that is objectionable to most plant workers. Unfortunately, the commercially supplied ozone generator or generating cells are not normally equipped with leakage detectors which can be used to effectively detect ozone leakage and thus enables an operator to attend to the problem.
It is therefore an object of the present invention to provide an ozone generator that does not have the drawbacks and shortcomings of the conventional ozone generators.
It is another object of the present invention to provide an apparatus to be used with a gas reactor for detecting any gas leakage from the reactor.
It is a further object of the present invention to provide an apparatus for use with a gas reactor that can be easily added to the reactor for detecting any gas leakage.
It is still another object of the present invention to provide an apparatus for use with an ozone generator that can be used effectively to detect any ozone leakage from the generator.
It is another further object of the present invention to provide an apparatus for use with an ozone generator that consists of simple flow sensors that are mounted to an inlet and an outlet of an ozone generator.
It is yet another object of the present invention to provide an apparatus for use with an ozone generator that utilizes flow sensors mounted to the inlet conduit and the outlet conduit of the generator such that the outputs from the sensors can be monitored.
It is still another further object of the present invention to provide an apparatus for use with an ozone generator that utilizes flow sensors which are mounted to the inlet conduit and the outlet conduit of the generator such that the outputs from the sensors can be monitored by a logic device.
It is yet another further object of the present invention to provide a method for monitoring ozone leakage from an ozone generator by mounting flow sensors to the inlet and the outlet of the generator and comparing the volume of gases flowing in and out of the generator.